Ink composition for ink jet recording, recording method and recorded matter

ABSTRACT

There is provided an ink composition that, even on various recording media, especially gloss paper of a printing paper base, can yield an image having excellent gloss, can realize good recovery from clogging and handleability of recorded matter, and, at the same time, can realize excellent ejection stability and color reproduction. The ink composition for ink jet recording comprises at least a colorant, water, an alkanediol, and a surfactant, wherein the alkanediol comprises a water soluble 1,2-alkanediol and a water soluble alkanediol having a hydroxyl group at both ends of its main chain, and the surfactant is a polyorganosiloxane.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention provides an ink composition for ink jet recording,which, even on various recording media, especially gloss paper of aprinting paper base, can yield images having excellent gloss and colorreproduction and, at the same time, can realize excellent ejectionstability and recovery from clogging, and a method for ink jet recordingusing the ink composition.

2. Background Art

Ink jet recording is a printing method wherein droplets of an ink areejected and deposited on recording media, such as paper, to performprinting. An innovative advance of a recent ink jet recording techniquehas made it possible to realize the production of images having qualitycomparable to images produced by silver salt photography or imagesyielded by high-definition printing realized only by offset printing.This trend has led to the development of inks for ink jet recording thatcan realize images having a high level of gloss comparable to the glossof images produced by silver salt photography, using the so-calledspecialty papers which are recording media having a high level of glosscomparable to photographic paper, art paper and the like used in thefield of silver salt photography and offset printing. Further, inks forink jet recording which can realize image quality comparable to theimage quality of images produced by silver salt photography even onplain paper, have also been developed.

Inks, which have been generally used for ink jet recording, arewater-based inks that comprise water as a main component and a colorantand various additives. Regarding the colorant, the development ofpigment-based inks utilizing the properties of the pigment has recentlybeen forwarded because pigments are superior to dyes in weatherfastnessproperties such as lightfastness, gasfastness, waterfastness, andmoisturefastness. For example, Japanese Patent Laid-Open No. 194500/2005discloses a pigment-based ink having feathering- or bleeding-freeproperties and excellent gloss on specialty papers that have beenrealized by using a polysiloxane compound as a surfactant and adding analkanediol such as 1,2-hexanediol as a solubilizer additive to the ink.Further, Japanese Patent Laid-Open Nos. 72905/2001 and 12583/2003disclose an ink containing 1,2-hexanediol, which is a water solublealkanediol, and 1,5-pentanediol, which is a water soluble alkanediolhaving a hydroxyl group at both ends of its main chain, as additives.The claimed advantage of this ink is feathering- or bleeding-freeproperties on plain papers.

In recent years, spreading of a technique for image formation fromdigital data and consideration to natural environment have led to needs,particularly in photographic markets, for ink jet printed matter thatcan reduce the necessary amount of chemical substances to be used andthe amount of waste liquid to be treated, and an ink jet recordingsystem has begun to be applied also in minilab shops. In minilab, colorreproduction and stable reproduction of ink jet recorded matter of aprinting paper base similar to silver salt photographs are required, andglossy impression comparable to that of silver salt photographs is alsorequired. Further, in recent years, services in which such recordedmatter is put into a glassed-in frame immediately after printing and isthen handed to a customer on site or is then sent to a customer by mail,are advanced. Putting the ink jet recorded matter into a glassed-inframe immediately after printing, however, sometimes causes dewformation on the glass in the case of some recording media and serviceenvironment.

The use of a high-penetration ink containing the above polysiloxanesurfactant and 1,2-hexanediol as a solubilizer for the polysiloxanesurfactant from the viewpoint of solving the above problem can improvethe glossy impression, but sometimes poses a problem of thehandleability of the ink jet recorded matter.

SUMMARY OF THE INVENTION

The present inventors have now found that the addition of a combinationof two specific alkanediols with a polyorganosiloxane compound as asurfactant to ink can realize an ink composition that, even on variousrecording media, especially gloss paper of a printing paper base, canyield an image having excellent gloss, can realize good recovery fromclogging and handleability of recorded matter, and, at the same time,can realize excellent ejection stability and color reproduction. Thepresent invention has been made based on such finding. The expression“handleability of recorded matter” as used herein means that, whenrecorded matter is put into a frame formed of, for example, a glassplate or an acrylic plate, an ink solvent left from the recorded matteris not deposited onto the frame.

Accordingly, an object of the present invention is to provide an inkcomposition that, even on various recording media, especially glosspaper of a printing paper base, can yield an image having excellentgloss, can realize good recovery from clogging and handleability ofrecorded matter, and, at the same time, can realize excellent ejectionstability and color reproduction.

According to the present invention, there is provided an ink compositionfor ink jet recording, comprising at least a colorant, water, analkanediol, and a surfactant, wherein

the alkanediol comprises a water soluble 1,2-alkanediol and a watersoluble alkanediol having a hydroxyl group at both ends of its mainchain and

the surfactant is a polyorganosiloxane.

The present invention can realize an ink composition that, even onvarious recording media, especially gloss paper of a printing paperbase, can yield an image having excellent gloss, can realize goodrecovery from clogging and handleability of recorded matter, and, at thesame time, can realize excellent ejection stability and colorreproduction.

DETAILED DESCRIPTION OF THE INVENTION

The ink composition for ink jet recording according to the presentinvention comprises a colorant, water, an alkanediol, and a surfactantas indispensable ingredients. The alkanediol comprises two types ofalkanediols, that is, a water soluble 1,2-alkanediol and a water solublealkanediol having a hydroxyl group at both ends of its main chain. Thesurfactant is a polyorganosiloxane. The individual ingredients will bedescribed.

<Alkanediol>

The alkanediol used in the ink composition for ink jet recordingaccording to the present invention comprises at least two types ofalkanediols, that is, a water soluble 1,2-alkanediol and a water solublealkanediol having a hydroxyl group at both ends of its main chain. Theuse of these two specific types of alkanediols together with asurfactant, which will be described later, can realize an inkcomposition that, even on a porous gloss paper of a printing paper base,which has excellent ink solvent absorption, but on the other hand, anink solvent is sometimes left from recorded matter under someenvironment, can realize excellent glossy impression and anti-cloggingproperties and can suppress the leaving of the ink solvent from therecorded matter. Further, even when the ink composition is applied toplain paper, the sharpness of character edge can be improved and, thus,the ink composition is suitable for applications of recorded matterssuch as covenants with small font sizes. The reason why these advantagescan be realized has not been elucidated yet but is considered asfollows. As described above, in conventional high-penetration inks forink jet recording, the use of 1,2-hexanediol or 4-methyl-1,2-pentanediolis preferred from the viewpoint of lowering the surface tension toimprove a glossy impression. In order to realize very low surfacetension by adding only a water soluble 1,2-alkanediol such as1,2-hexanediol, however, the addition of a large amount of the1,2-alkanediol is necessary. For example, the surface tension of a 15 wt% aqueous solution of 1,2-hexanediol or 4-methyl-1,2-pentanediol is 25to 26 mN/m. The addition of this substance increases the viscosity ofthe ink, and, thus, ink weight of dots is reduced. Accordingly, the inkweight of dots cannot be accurately regulated without difficulties. As aresult, upon the ejection of ink from the head, unfavorable phenomenasometimes occur such as a shift in impact position of ink droplets,misting of ink, and poor print durability, often leading to loweredcolor development, deteriorated graininess, uneven coagulation andcolor-to-color bleeding which are causative of printing failure. On theother hand, the addition of only a water soluble alkanediol having ahydroxyl group at both ends of its main chain such as 1,5-pentanedioldisadvantageously results in deteriorated glossy impression, forexample, because the surface tension of a 15 wt % aqueous solution of1,5-pentanediol is not less than 35 mN/m.

When the water soluble 1,2-alkanediol and the water soluble diol havinga hydroxyl group at both ends of its main chain are simultaneouslyincorporated, an improvement in glossy impression and rendering thesurface tension of ink compatible with the output frequency of inkdroplets suitable in ink jet recording can be realized, because thewater soluble 1,2-alkanediol can effectively lower the surface tensionto improve the glossy impression while the water soluble diol having ahydroxyl group at both ends of its main chain can regulate the surfacetension at each frequency. Such regulation can improve the accuracy ofejection weight and the impact accuracy of ink droplets on recordedmatter.

In the present invention, the water soluble 1,2-alkanediol is preferablyan optionally branched 1,2-alkanediol having 5 or 6 carbon atoms, andexamples thereof include 4-methyl-1,2-pentanediol, 1,2-pentanediol,3,3-dimethyl-1,2-butanediol, and 1,2-hexanediol. Among them,1,2-hexanediol and/or 4-methyl-1,2-pentanediol are particularlypreferred.

The content of the water soluble 1,2-alkanediol is preferably not lessthan 3% by weight, more preferably 6 to 15% by weight, based on thewhole ink composition. When the content of water soluble 1,2-alkanediolis in the above-defined range, lowering and/or fluctuation of inkviscosity in low-temperature and high-temperature states can besuppressed, contributing to stable ink ejection.

The water soluble alkanediol having a hydroxyl group at both ends of itsmain chain preferably contains an optionally branched alkanediol having3 to 10 carbon atoms, and examples thereof include 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Among them,1,5-pentanediol is particularly preferred from the viewpoints ofviscosity and durability of members used in an ink jet recordingapparatus.

The content of the water soluble alkanediol having a hydroxyl group atboth ends of its main chain is preferably 3 to 15% by weight, morepreferably 3.0 to 6.0% by weight, based on the whole ink composition.

When the content of the water soluble alkanediol is in the above-definedrange, the lowering of content of the wetting agent, for example,glycerin, as a main component of the ink solvent, which is left from therecorded matter, and/or the leaving of the wetting agent can beeffectively suppressed. Further, the anti-clogging property can beimproved without containing the wetting agent in an amount exceeding 15%by weight. That is, the addition of the water soluble alkanediol in theabove-defined amount range is effective in both viscosity lowering andprevention of the solvent from being left.

In the present invention, the content ratio of the water soluble1,2-alkanediol to the water soluble alkanediol having a hydroxyl groupat both ends of its main chain is preferably 10:1 to 1:1 on a weightbasis. When both the alkanediols are mixed together at this definedratio range, printing of the ink on a gloss paper of a printing paperbase can realize an improvement in glossy impression by virtue oflowered surface tension and stable ejection by virtue of the regulationof surface tension at a specific frequency.

In printing on plain paper, the edge sharpness of small fonts can beimproved through an improvement in good ink droplet impact positionaccuracy.

Further, in the present invention, the ink composition may contain, as apenetration solvent, 1,2-alkanediols having 5 to 10 carbon atoms and/or1,2-alkanediols having 3 to 10 carbon atoms and/or lactams and/orlactones, to which a polyoxyethylene chain and/or a polypropylene chainhave been added.

<Surfactant>

The ink composition for ink jet recording according to the presentinvention contains a surfactant as an indispensable ingredient. When therecording medium used has on its surface a resin coating receptive toink, the use of a surfactant in the ink composition for ink jetrecording can realize images having excellent gloss even on recordingmedia, in which greater importance is attached to a glossy impression,for example, photographic paper.

In the present invention, organopolysiloxane surfactants are used as thesurfactant. The use of the organopolysiloxane surfactant is advantageousin that, since the above specific two alkanediols are contained, thesolubility of the surfactant in the ink is improved to suppress theoccurrence of insolubles and the like, whereby an ink composition havingbetter ejection stability can be realized.

More preferably, the ink composition contains one or at least twocompounds represented by formula as the organopolysiloxane surfactant:

wherein R represents a hydrogen atom or a methyl group; a is an integerof 7 to 11; m is an integer of 20 to 70; and n is an integer of 2 to 5.When such specific organopolysiloxane surfactants are used, the surfaceof the recorded matter having concaves and convexes can be furtherrendered smooth.

In another preferred embodiment of the present invention, one or atleast two compounds represented by the above formula, wherein Rrepresents a hydrogen atom or a methyl group, a is an integer of 2 to 5,m is an integer of 20 to 70, and n is an integer of 2 to 4, may becontained as the polysiloxane compound.

When the above polyorganosiloxane compounds are contained, preferably, apolysiloxane compound represented by the above formula, wherein Rrepresents a hydrogen atom or a methyl group; a is an integer of 9 to13; m is an integer of 2 to 4; and n is 1 or 2, is further contained asthe surfactant. The combined use of this polysiloxane compound canrender the surface of the recorded matter having concaves and convexesmore smooth.

The reason why the incorporation of the above specificpolyorganosiloxane compounds can render the recorded matter surfacehaving concaves and convexes smooth, is considered as follows.Specifically, for example, in an aqueous solution comprising 20% byweight of glycerin (glycerol), 10% by weight of 1,2-hexanediol, and 0.1%by weight of the above surfactant, the surface tension of the aqueoussolution at 1 Hz is not more than 25 mN/m. That is, the incorporation ofthe above surfactant can realize a very low surface tension of theglycol-containing aqueous solution. When Surfynol 465, which is anacetylene glycol surfactant, is brought to an aqueous solution havingthe same composition as described above, the surface tension of theaqueous solution is not less than 25 mN/m.

Such surfactants may be commercially available products, and examplesthereof include KF-954A, KF-353A, KF6017, X-22-6551 and AW-3 (all theabove products being manufactured by The Shin-Etsu Chemical Co., Ltd.).

The content of the surfactant in the ink composition according to thepresent invention is preferably 0.01 to 2.00% by weight, more preferably0.05 to 0.50% by weight. In particular, when the surfactant wherein Rrepresents a methyl group is used, preferably, the content of thesurfactant is larger than the case where the surfactant wherein Rrepresents H is used.

Other surfactants, specifically fluorosurfactants, acetylene glycolsurfactants, anionic surfactants, nonionic surfactants, amphotericsurfactants and the like, may be further added to the ink compositionaccording to the present invention.

Examples of acetylene glycol surfactants among these other surfactantsinclude 2,4,7,9-tetramethyl-5-decyne-4,7-diol,3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, or2,4-dimethyl-5-hexyn-3-ol. Acetylene glycol surfactants may also becommercially available products. Examples thereof include Olfine E1010,Olfine STG, or Olfine Y (tradename, manufactured by Nissin ChemicalIndustry Co., Ltd.) and Surfynol 61, Surfynol 104, Surfynol 82, Surfynol465, Surfynol 485 or Surfynol TG (tradename, manufactured by AirProducts and Chemicals Inc.).

<Colorant>

Any of dyes and pigments may be used as the colorant in the inkcomposition for ink jet recording according to the present invention.However, pigments are preferred from the viewpoints of lightfastness andwaterfastness.

Inorganic pigments and organic pigments are usable as the pigment. Theinorganic pigments and the organic pigments may be used either solely oras a mixture of two or more. Inorganic pigments include, for example, inaddition to titanium oxide and iron oxide, carbon blacks produced byknown processes, such as contact, furnace, and thermal processes.Organic pigments usable herein include azo pigments (including azo lake,insoluble azo pigment, condensed azo pigment, and chelate azo pigment),polycyclic pigments (for example, phthalocyanine, perylene, perinone,anthraquinone, quinacridone, dioxazine, thioindigo, isoindolinone, andquinophthalone pigments), dye-type chelate pigments (for example, basicdye-type chelate pigments and acid dye-type chelate pigments), nitropigments, nitroso pigments, and aniline blacks.

Pigments used may be properly selected depending upon the type (color)of the ink composition to be prepared using the pigment dispersionliquid according to the present invention. Examples of pigments foryellow ink compositions include C.I. Pigment Yellow 1, C.I. PigmentYellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. PigmentYellow 14, C.I. Pigment Yellow 16, C.I. Pigment Yellow 17, C.I. PigmentYellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I. PigmentYellow 83, C.I. Pigment Yellow 93, C.I. Pigment Yellow 95, C.I. PigmentYellow 97, C.I. Pigment Yellow 98, C.I. Pigment Yellow 109, C.I. PigmentYellow 110, C.I. Pigment Yellow 114, C.I. Pigment Yellow 128, C.I.Pigment Yellow 129, C.I. Pigment Yellow 138, C.I. Pigment Yellow 139,C.I. Pigment Yellow 147, C.I. Pigment Yellow 150, C.I. Pigment Yellow151, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. PigmentYellow 180, and C.I. Pigment Yellow 185. They may be used either solelyor in a combination of two or more. The use of one or at least twopigments selected from the group consisting of C.I. Pigment Yellow 74,C.I. Pigment Yellow 110, C.I. Pigment Yellow 128, and C.I. PigmentYellow 147 is particularly preferred. Examples of pigments for magentaink compositions include C.I. Pigment Red 5, C.I. Pigment Red 7, C.I.Pigment Red 12, C.I. Pigment Red 48 (Ca), C.I. Pigment Red 48 (Mn), C.I.Pigment Red 57 (Ca), C.I. Pigment Red 57:1, C.I. Pigment Red 112, C.I.Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 168, C.I.Pigment Red 184, C.I. Pigment Red 202, C.I. Pigment Red 209, and C.I.Pigment Violet 19. They may be used either solely or in a combination oftwo or more. The use of one or at least two pigments selected from thegroup consisting of C.I. Pigment Red 122, C.I. Pigment Red 202, C.I.Pigment Red 209, and C.I. Pigment Violet 19 is particularly preferred.Examples of pigments for cyan ink compositions include C.I. Pigment Blue1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15:2,C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 15:34,C.I. Pigment Blue 16, C.I. Pigment Blue 22, and C.I. Pigment Blue 60;and C.I. Vat Blue 4 and C.I. Vat Blue 60. They may be used either solelyor in a combination of two or more. The use of C.I. Pigment Blue 15:3and/or C.I. Pigment Blue 15:4 is particularly preferred. C.I. PigmentBlue 15:3 is still more preferred. Examples of pigments for black inkcompositions include inorganic pigments, for example, carbon blacks(C.I. Pigment Black 7) such as furnace black, lamp black, acetyleneblack, and channel black and iron oxide pigments; and organic pigments,for example, aniline black (C.I. Pigment Black 1).

In the present invention, preferably, the pigment is a pigment which hasbeen kneaded with a dispersant which will be described later. However,pigments not subjected to surface treatment can also form excellentcolor images.

<Dispersant>

The ink composition according to the present invention preferablycomprises a copolymer resin of a hydrophobic monomer and a hydrophilicmonomer as a dispersant for dispersing a colorant. The copolymer resinis adsorbed to a pigment to improve the dispersibility of the pigment.

Specific examples of hydrophobic monomers include methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propylacrylate, n-propyl methacrylate, iso-propyl acrylate, iso-propylmethacrylate, n-butyl acrylate, n-butyl methacrylate, sec-butylacrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butylmethacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-octyl acrylate,n-octyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate,2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl acrylate, decylmethacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate,stearyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,2-dimethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate,2-diethylaminoethyl acrylate, 2-diethylaminoethyl methacrylate, glycidylacrylate, glycidyl methacrylate, allyl acrylate, allyl methacrylate,cyclohexyl acrylate, cyclohexyl methacrylate, phenyl acrylate, phenylmethacrylate, nonylphenyl acrylate, nonylphenyl methacrylate, benzylacrylate, benzyl methacrylate, dicyclopentenyl acrylate, dicyclopentenylmethacrylate, bornyl acrylate, bornyl methacrylate, 1,3-butanedioldiacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate,1,4-butanediol dimethacrylate, ethylene glycol diacrylate, ethyleneglycol dimethacrylate, diethylene glycol diacrylate, diethylene glycoldimethacrylate, triethylene glycol diacrylate, triethylene glycoldimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, polyethylene glycol diacrylate, polyethylene glycoldimethacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate,1,6-hexanediol dimethacrylate, dipropylene glycol diacrylate,dipropylene glycol dimethacrylate, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, glycerol acrylate, glycerolmethacrylate, styrene, methylstyrene, and vinyltoluene. They may be usedeither solely or as a mixture of two or more.

Specific examples of hydrophilic monomers include acrylic acid,methacrylic acid, maleic acid, and itaconic acid.

The copolymer resin of a hydrophobic monomer and a hydrophilic monomeris preferably at least any one of styrene-(meth) acrylic acid copolymerresins, styrene-methylstyrene-(meth)acrylic acid copolymer resins,styrene-maleic acid copolymer resins, (meth)acrylic acid-(meth)acrylicester copolymer resins, and styrene-(meth)acrylic acid-(meth)acrylicester copolymer resins, from the viewpoints of simultaneously satisfyingcolor image gloss, bronzing prevention, and ink composition storagestability requirements and, at the same time, forming color imageshaving better gloss.

The copolymer resin may be a resin (styrene-acrylic acid resin)comprising a polymer produced by reacting styrene with acrylic acid oran acrylic ester. Alternatively, the copolymer resin may be an acrylicacid-type water soluble resin. Alternatively, salts thereof, forexample, sodium, potassium, or ammonium salts thereof, may also be used.

The content of the copolymer resin is preferably 10 to 50 parts byweight, more preferably 10 to 35 parts by weight, based on 100 parts byweight of the pigment, from the viewpoints of simultaneously satisfyingcolor image gloss, bronzing prevention, and ink composition storagestability requirements and, at the same time, forming color imageshaving better gloss.

Examples of surfactants which are preferred as dispersants includeanionic surfactants such as fatty acid salts, higher alkyldicarboxylicacid salts, higher alcohol sulfuric ester salts, higher alkylsulfonicacid salts, condensates of higher fatty acids with amino acids,sulfosuccinic ester salts, naphthenic acid salts, liquid fatty oilsulfuric ester salts, and alkylallylsulfonic acid salts; cationicsurfactants such as fatty acid amine salts, quaternary ammonium salts,sulfonium salts, and phosphoniums; and nonionic surfactants such aspolyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitanalkyl esters, and polyoxyethylene sorbitan alkyl esters. It is needlessto say that the above surfactants, when added to the ink composition,can function also as a surfactant. In this case, however, the surfactantshould be added so that the contact angle of the recording medium withthe ink composition falls within the above defined range.

<Water and Other Ingredients>

The ink composition for ink jet recording according to the presentinvention comprises the above specific solvent and surfactant, othervarious additives and further contains water as a solvent. Water ispreferably pure water obtained by ion exchange, ultrafiltration, reverseosmosis, distillation or the like, or ultrapure water. These waters,which have been sterilized, for example, by ultraviolet irradiation orby addition of hydrogen peroxide, are particularly preferred becausethey can prevent the growth of mold or bacteria in the ink compositionfor a long period of time.

The ink composition according to the present invention may furthercomprise an organic amine. The organic amine can enhance the capabilityof wetting a recording face in a recording medium or the like in theformation of a recorded image to enhance the ink penetration. Further,when the organic amine is contained, pH of the ink composition caneasily be adjusted to a suitable range. The organic amine is preferablya tertiary amine.

For example, alkanolamines such as triethanolamine may be mentioned asthe tertiary amine. The pH value of the ink composition according to thepresent invention is preferably 8 to 12, particularly preferably 8 to10. When the pH value is in the above-defined range, a deterioration inmembers in contact with the ink can be prevented.

The content of the organic amine in the total weight of the inkcomposition is not less than 0.1% by weight. In this case, thecapability of the ink composition to wet a recording face, for example,in a recording medium in recorded image formation can be enhanced toenhance ink penetration. From the viewpoints of the ejection stability,storage stability, and high speed printing of the ink, the content ofthe organic amine is preferably 0.1 to 8.0% by weight, more preferably0.5 to 5.0% by weight, still more preferably 1.0 to 3.0% by weight.

Further, the ink composition according to the present inventionpreferably comprises a penetrating agent in addition to the aboveingredients.

Glycol ethers are suitable as the penetrating agent.

Specific examples of glycol ethers usable herein include ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethyleneglycol mono-iso-butyl ether, ethylene glycol mono-tert-butyl ether,ethylene glycol monomethyl ether acetate, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycolmono-n-propyl ether, diethylene glycol mono-iso-propyl ether, diethyleneglycol mono-n-butyl ether, diethylene glycol mono-tert-butyl ether,triethylene glycol mono-n-butyl ether, propylene glycol monomethylether, propylene glycol monoethyl ether, propylene glycol mono-n-propylether, propylene glycol mono-iso-propyl ether, propylene glycolmono-n-butyl ether, propylene glycol mono-tert-butyl ether, dipropyleneglycol monomethyl ether, dipropylene glycol monoethyl ether, dipropyleneglycol mono-n-propyl ether, dipropylene glycol-iso-propyl ether,dipropylene glycol mono-n-butyl ether, dipropylene glycolmono-tert-butyl ether, and 1-methyl-1-methoxybutanol. They may be usedeither solely or as a mixture of two or more.

Among the above glycol ethers, alkyl ethers of polyhydric alcohols arepreferred. Particularly preferred are ethylene glycol monoethyl ether,ethylene glycol mono-n-butyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether,triethylene glycol monomethyl ether, triethylene glycol monoethyl ether,or triethylene glycol mono-n-butyl ether. More preferred are triethyleneglycol mono-n-butyl ether.

The addition amount of the penetrating agent may be properly determinedbut is preferably about 0.1 to 30% by weight, more preferably about 1 to20% by weight.

Preferably, the ink composition according to the present inventionfurther comprises a solubilizer for a recording medium in addition tothe above ingredients.

Pyrrolidones such as N-methyl-2-pyrrolidone and/or lactones such asγ-butyrolactone are suitable as a solubilizer for a recording medium.The addition amount of the solubilizer for a recording medium may beproperly determined but is preferably about 0.1 to 30% by weight, morepreferably about 1 to 20% by weight.

Preferably, the ink composition for ink jet recording according to thepresent invention comprises a wetting agent. Polyhydric alcohols and/orsaccharides are suitable as the wetting agent. Specific examples ofpolyhydric alcohols include glycerin, ethylene glycol, diethyleneglycol, triethylene glycol, and trimethylolpropane. Specific examples ofsaccharides include monosaccharides, disaccharides, oligosaccharides(including trisaccharides and tetrasaccharides), and polysaccharides,and preferred examples thereof include glucose, mannose, fructose,ribose, xylose, arabinose, galactose, aldonic acid, glucitol, sorbit,maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose. Herethe term “polysaccharide” used herein means saccharides in the broadsense as including substances which exist widely in the world of nature,such as alginic acid, α-cyclodextrin and cellulose. Derivatives of thesesaccharides include reducing sugars of the above saccharides (forexample, sugar alcohols represented by the general formulaHOCH₂(CHOH)_(n)CH₂OH wherein n is an integer of 2 to 5), oxidized sugars(for example, aldonic acid and uronic acid), amino acid, and thiosugars.Sugar alcohols are particularly preferred, and specific examples thereofinclude maltitol, sorbitol, and xylitol. Further, commercially availableproducts such as HS-500 (manufactured by HAYASHIBARA SHOJI, INC.) arealso suitable. Hyaluronates may be products commercially available as a1% aqueous solution of sodium hyaluronate (molecular weight 350000).Trimethylolpropane and 1,2,6-hexatriol are also suitable.

The addition amount of the wetting agent is preferably 3 to 30% byweight, more preferably about 3 to 20% by weight, still more preferably3 to 10% by weight. It would be apparent to a person having ordinaryskill in the art that a part of the penetration solvent functions alsoas a wetting agent.

In the present invention, the content ratio of the water solublealkanediol having a hydroxyl group at both ends of its main chain to thewetting agent is preferably 1:1 to 1:10 on a weight basis. When themixing ratio is in the above-defined range, dew formation caused byseparation of the wetting agent from gloss paper of a printing paperbase immediately after recording can be suppressed, and, further, thelow viscosity can prevent clogging.

If necessary, other additives, for example, nozzle clogging preventives,preservatives, antioxidants, electric conductivity adjustors, pHadjustors, viscosity modifiers, surface tension modifiers, and oxygenabsorbers, may be added to the ink composition according to the presentinvention.

For example, sodium benzoate, pentachlorophenol sodium,2-pyridinethiol-1-oxide sodium, sodium sorbate, sodium dehydroacetate,and 1,2-dibenzothiazolin-3-one (Proxel CRL, Proxel BND, Proxel GXL,Proxel XL-2, and Proxel TN, manufactured by ICI) may be used aspreservatives and antimolds.

Examples of pH adjustors, solubilizers, or antioxidants usable hereininclude: amines such as diethanolamine, triethanolamine, propanolamine,and morpholine, and modification products thereof; inorganic salts suchas potassium hydroxide, sodium hydroxide, and lithium hydroxide;ammonium hydroxide; quaternary ammonium hydroxides such astetramethylammonium; salts of carbonic acid such as potassium carbonate,sodium carbonate, and lithium carbonate; salts of phosphoric acid, suchas potassium phosphate, sodium phosphate, and lithium phosphate;N-methyl-2-pyrrolidone; urea compounds such as urea, thiourea, andtetramethylurea; allophanates such as allophanate and methylallophanate; biurets such as biuret, dimethylbiuret, andtetramethylbiuret; and L-ascorbic acid and salts thereof.

The ink composition according to the present invention may contain anadditional antioxidant and an ultraviolet absorber, and examples thereofinclude: Tinuvin 328, Tinuvin 900, Tinuvin 1130, Tinuvin 384, Tinuvin292, Tinuvin 123, Tinuvin 144, Tinuvin 622 and Tinuvin 770 manufacturedby Ciba Specialty Chemicals, K.K.; Irgacor 252 and Irgacor 153; Irganox1010, Irganox 1076, and Irganox 1035; MD 1024; and lanthanide oxides.

The ink composition according to the present invention can be producedby dispersing and mixing the above ingredients by a suitable method.Preferably, an ink solution is prepared by first mixing the pigment, thepolymeric dispersant, and water together by a suitable dispergator, forexample, a ball mill, a sand mill, an attritor, a roll mill, an agitatormill, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a jetmill, or an angmill to prepare a homogeneous pigment dispersion liquid,then adding, for example, separately prepared resins (resin emulsion),water, water soluble organic solvents, saccharides, pH adjustors,preservatives and antimolds, and satisfactorily dissolving thecomponents. After the satisfactory stirring, the mixture is filtered forthe removal of coarse particles and foreign matter causative of cloggingto prepare a contemplated ink composition.

Method for Ink Jet Recording

The method for ink jet recording according to the present inventioncomprises ejecting droplets of the ink composition and depositing thedroplets onto a recording medium to perform printing. In this method,the ejected ink droplets are deposited onto the recording medium so thatdots are superimposed on top of each other. In the recording methodaccording to the present invention, preferably, printing paper forrunning-on is used as the recording medium. Even when the specificrecording medium is used, images possessing excellent glossiness andgood color reproduction can be realized.

Further, in the method for ink jet recording according to the presentinvention, preferably, droplets of the ink composition are ejected sothat dots in a vertical direction are alternately arranged relative to ascanning direction of the recording head. In the formation of dots inthis checked pattern, when the ink composition of the present inventionis used, uneven coagulation can be significantly improved as comparedwith the conventional ink composition.

EXAMPLES

The following Examples further illustrate the present invention.However, it should be noted that the present invention is not limited tothese Examples.

<Preparation of Ink Compositions>

Ingredients were mixed together according to the formulations shown inTable 1, and the mixtures were filtered through a 10-μm membrane filterto prepare inks.

TABLE 1 Example 1 Example 2 Ink set 1 Ink set 2 Composition 1Y 1M 1C 1B2Y 2M 2C 2B Colorant C.I. Pigment 3.0 — — — 3.0 — — — Yellow 74 C.I.Pigment — 3.0 — — — 3.0 — — Red 122 C.I. Pigment — — 3.0 — — — 3.0 —Blue 15:4 C.I. Pigment — — — 3.0 — — — 3.0 Black 7 Styrene-acrylic resin1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Alkanediol 1,2-Hexanediol 6.0 6.0 6.06.0 12   12   12   12   1,5-Pentanediol 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Surfactant Polysiloxane 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 surfactant(note 1) Triethanolamine 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Glycerin 12.0 12.0  12.0  12.0  6.0 6.0 6.0 6.0 Pure water Balance Balance BalanceBalance Balance Balance Balance Balance Total 100    100    100   100    100    100    100    100    Example 3 Example 4 Ink set 3 Ink set4 Composition 3Y 3M 3C 3B 4Y 4M 4C 4B Colorant C.I. Pigment 3.0 — — —3.0 — — — Yellow 74 C.I. Pigment — 3.0 — — — 3.0 — — Red 122 C.I.Pigment — — 3.0 — — — 3.0 — Blue 15:4 C.I. Pigment — — — 3.0 — — — 3.0Black 7 Styrene-acrylic resin 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Alkanediol1,2-Hexanediol 12   12   12   12   10   10   10   10   1,5-Pentanediol6.0 6.0 6.0 6.0 5.0 5.0 5.0 5.0 Surfactant Polysiloxane 0.1 0.1 0.1 0.10.1 0.1 0.1 0.1 surfactant (note 1) Triethanolamine 0.9 0.9 0.9 0.9 0.90.9 0.9 0.9 Glycerin 6.0 6.0 6.0 6.0 12.0  12.0  12.0  12.0  Pure waterBalance Balance Balance Balance Balance Balance Balance Balance Total100    100    100    100    100    100    100    100    ComparativeExample 1 Comparative Example 2 Ink set 5 Ink set 6 Composition 1Y 1M 1C1B 2Y 2M 2C 2B Colorant C.I. Pigment 3.0 — — — 3.0 — — — Yellow 74 C.I.Pigment — 3.0 — — — 3.0 — — Red 122 C.I. Pigment — — 3.0 — — — 3.0 —Blue 15:4 C.I. Pigment — — — 3.0 — — — 3.0 Black 7 Styrene-acrylic resin1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Alkanediol 1,2-Hexanediol 3.0 3.0 3.03.0 12   12   12   12   1,5-Pentanediol 3.0 3.0 3.0 3.0 — — — —Surfactant Surfynol 465 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Triethanolamine0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Glycerin 12.0  12.0  12.0  12.0  12  12   12   12   Pure water Balance Balance Balance Balance BalanceBalance Balance Balance Total 100    100    100    100    100    100   100    100    Comparative Example 3 Ink set 7 Composition 3Y 3M 3C 3BColorant C.I. Pigment 3.0 — — — Yellow 74 C.I. Pigment — 3.0 — — Red 122C.I. Pigment — — 3.0 — Blue 15:4 C.I. Pigment — — — 3.0 Black 7Styrene-acrylic resin 1.2 1.2 1.2 1.2 Alkanediol 1,2-Hexanediol 12  12   12   12   1,5-Pentanediol 3.0 3.0 3.0 3.0 Surfactant Surfynol 4650.1 0.1 0.1 0.1 Triethanolamine 0.9 0.9 0.9 0.9 Glycerin 3.0 3.0 3.0 3.0Pure water Balance Balance Balance Balance Total 100    100    100   100    (note 1): The polysiloxane surfactant is AW-3: X-22-6551 = 9:1.

The styrene-acrylic acid resin in the table is a copolymer having amolecular weight of 1600 and an acid value of 150.

<Evaluation>

Ejection Stability

An ink jet printer (PX-G900, manufactured by Seiko Epson Corporation)was provided. For each of the inks prepared above, a one-raster ruledline pattern was continuously printed on photographic paper at 5° C.(low temperature) by depositing ink droplets on three dot weight levelsof 3 ng, 7 ng and 14 ng. Thereafter, the thickness of the ruled line in1000 printed sheets was observed and was evaluated based on thefollowing criteria.

A: A reduction in the width of the ruled line of less than 10% onaverage

B: A reduction in the width of the ruled line of not less than 10% onaverage

The results of evaluation were as shown in Table 2 below.

Recovery from Clogging

The ink jet printer as used above was provided. Each ink was loaded intothe head. After normal ejection of the ink through all nozzles wasconfirmed, in order to accelerate drying in nozzles, the ink cartridgewas removed, and the recording head was removed from the head cap,followed by standing in this state under an environment of 40° C. and20% RH for one week.

After the one-week standing, cleaning operation was repeated todetermine the number of cleaning operations required for all the nozzlesto normally eject the ink as in the initial state. The recovery fromnozzle clogging was evaluated according to the following criteria.

A: Recovered to substantially the initial state by performing thecleaning operation three times or less.

B: Recovered to substantially the initial state by performing thecleaning operation six times or less.

C: Recovered to substantially the initial state by performing thecleaning operation six times, then allowing the nozzles to stand for 6hr, and then further performing the cleaning operation once.

The results of evaluation were as shown in Table 2 below.

Edge Sharpness

Ink set 1 was loaded into an ink cartridge in the same ink jet printeras described above. “Futsushi Suisho, Kirei Modo (Plain PaperRecommended, Fine Mode)” was selected, and a Chinese character

(font size 8) was printed on XeroxP (manufactured by Xerox Corp.) with aresolution of 1440×720 dpi under setting of “Without Gloss Optimizer.”The printed matter was then allowed to stand at 25° C. for 24 hr and wasobserved. The results were evaluated according to the followingcriteria.

A: No collapse was observed in a part

in the Chinese character

.

B: Collapse was observed in a part

in the Chinese character

.

Likewise, the evaluation of color reproduction was carried out for inksets 2 to 7. The results of evaluation were as shown in Table 2.

Gloss

Ink set 1 was loaded into an ink cartridge in the same ink jet printeras used above. “Shashin Yoshi Suisho, Kirei Modo (Photographic PaperRecommended, Fine Mode)” was selected, and each ink was printed onphotographic paper <Kotaku (Glossy)> (manufactured by Seiko EpsonCorporation) at 100% duty to yield recorded matter with a resolution of1440×720 dpi. The 45-degree specular gloss of the recorded matter wasmeasured with a goniophotometer GP-200 (tradename: manufactured byMurakami Color Research Laboratory), and the gloss was evaluatedaccording to the following criteria.

Measuring conditions were set so that the sensitivity was 500 and the45-degree specular gloss of a standard black specular glass plate was42.5. The results of evaluation were as shown in Table 2 below.

A: A gloss of not less than 35

B: A gloss of less than 35

Anti-Dewing

Ink set 1 was loaded into an ink cartridge in the same ink jet printeras used above. “Shashin Yoshi Suisho, Kirei Modo (Photographic PaperRecommended, Fine Mode)” was selected, and each ink was printed onphotographic paper <Kotaku (Glossy)> (manufactured by Seiko EpsonCorporation) at 100% duty to yield recorded matter with a resolution of1440×720 dpi. The recorded matter was put into a glass frame immediatelyafter recording and, in this state, was allowed to stand in anenvironment of temperature 40° C. and humidity 65% for 3 days.Thereafter, the glass frame was visually inspected for dewing. Theresults were evaluated according to the following criteria.

A: Dewing was observed on glass surface.

B: Dewing was not observed on glass surface.

The results of evaluation were as shown in Table 2 below.

TABLE 2 Anti- Anti- Ejection clogging Edge dewing stability propertysharpness Gloss property Example 1 A A A A A Example 2 A A A A A Example3 A A A A A Example 4 A A A A A Comparative A A A B A Example 1Comparative B A B A B Example 2 Comparative A B A A A Example 3

1. An ink composition for ink jet recording, comprising at least acolorant, water, an alkanediol, and a surfactant, wherein the alkanediolcomprises a water soluble 1,2-alkanediol and a water soluble alkanediolhaving a hydroxyl group at both ends of its main chain, the surfactantis a polyorganosiloxane, and the water-soluble alkanediol having ahydroxyl group at both ends of its main chain is selected from the groupconsisting of 1,3-propanediol, 1,4-butanediol and 1,6-hexanediol.
 2. Theink composition for ink jet recording according to claim 1, wherein thewater soluble 1,2-alkanediol is an optionally branched 1,2-alkanediolhaving 5 or 6 carbon atoms.
 3. The ink composition for ink jet recordingaccording to claim 2, wherein the water soluble 1,2-alkanediol is1,2-hexanediol and/or 4-methyl-1,2-pentanediol.
 4. The ink compositionfor ink jet recording according to claim 1, wherein thepolyorganosiloxane comprises one or at least two compounds representedby the following formula:

wherein R represents a hydrogen atom or a methyl group; a is an integerof 7 to 11; m is an integer of 20 to 70; and n is an integer of 2 to 5.5. The ink composition for ink jet recording according to claim 1,wherein said polyorganosiloxane comprises one or at least two compoundsrepresented by the following formula:

wherein R represents a hydrogen atom or a methyl group; a is an integerof 2 to 5; m is an integer of 20 to 70; and n is an integer of 2 to 4.6. The ink composition for ink jet recording according to claim 4,wherein the surfactant further comprises a polyorganosiloxanerepresented by the following formula:

wherein R represents a hydrogen atom or a methyl group; a is an integerof 9 to 13; m is an integer of 2 to 4; and n is an integer of 1 or
 2. 7.The ink composition for ink jet recording according to claim 1, whereinthe water soluble 1,2-alkanediol is contained in an amount of not lessthan 6% by weight based on the whole ink composition.
 8. The inkcomposition for ink jet recording according to claim 1, wherein thewater soluble alkanediol having a hydroxyl group at both ends of itsmain chain is contained in an amount of not less than 3% by weight basedon the whole ink composition.
 9. The ink composition for ink jetrecording according to claim 1, wherein the addition amount ratio of thewater soluble 1,2-alkanediol to the water soluble alkanediol having ahydroxyl group at both ends of its main chain is 10:1 to 1:1 on a weightbasis.
 10. The ink composition for ink jet recording according to claim1, which further comprises a wetting agent.
 11. The ink composition forink jet recording according to claim 10, wherein said wetting agent isglycerin and/or sugar.
 12. The ink composition for ink jet recordingaccording to claim 10, wherein the wetting agent is contained in anamount of 3% to 20% by weight based on the whole ink composition. 13.The ink composition for ink jet recording according to claim 10, whereinthe addition amount ratio of the water soluble alkanediol having ahydroxyl group at both ends of its main chain to the wetting agent is1:1 to 1:10 on a weight basis.
 14. A method for ink jet recording,comprising the step of ejecting droplets of an ink composition anddepositing the droplets onto a recording medium to perform printing,wherein the ink composition is an ink composition for ink jet recordingaccording to claim
 1. 15. A recorded matter recorded by a method forinkjet recording according to claim 14.